1. Field of the Invention
The present invention relates to an on-board lighting system for an aircraft and relates more particularly to a servocontrolled optical lighting system for an aircraft, which is capable of performing at least some of the lighting functions, notably a combination of these functions, during the various phases of landing, taxiing and take off of the aircraft by night.
2. Description of the Relevant Art
In the prior art, runway lighting systems onboard aircraft consist of a set of several lighting devices which are activated according to the phases of flight or taxiing of the aircraft. The lighting system in its entirety is thus capable of offering a taxiing function, generally referred to by its English name of “Taxi Light”, a turn off function, generally known by its English name of “Runway TurnOff Light”, a takeoff function (“TakeOff Light”), and a landing function (“Landing Light”).
These functions are performed by a set of separate lights fixed to the landing gear strut and in the leading edge of the wings, at the wing root or under the wing in the case of certain retractable lights.
By night, during the phases of landing, taking off, taxiing along the runway or along the taxiway, these various lighting systems are used in succession or simultaneously in order to allow the pilot to identify the space in which he needs to move around by night.
The distinct lights involved in the makeup of the lighting system are capable of emitting beams of light the intensity distribution and aim of which are tailored to the requirement in terms of pilot visibility.
In the context of lighting systems onboard airplanes, during the approach phase, the landing lights are aimed along the rectilinear glide slope of the airplane. During this phase, the zone that is to be illuminated corresponds to the point on the runway at which the airplane is to touch down. This is because this is the spot that the pilot needs to look at.
During the landing, and more particularly during the touch down phase (the English expression “touch down” is widely used) and more precisely before the wheels of the main landing gear touch the runway, the attitude of the airplane varies. The path followed by the airplane rounds off to become tangential to the runway.
Soon after this touch down phase, the front landing gear comes into contact with the ground. It is then the takeoff lights that take over, their aim being substantially parallel to the ground. These lights illuminate the ground as far ahead of the airplane as possible. During this phase, the zone that needs to be illuminated corresponds to the end of the runway.
During the approach and landing phases, the beam of light delivered by the lighting system has a spatial distribution and light intensity that remains the same. This spatial distribution is collimated in the direction of aim.
During the taxiing phase, it is the taxi lights and runway turn off lights that are used on the taxiways in order to leave or join the runway. During these phases, the lighting is characterized by a light distribution that is widely spread in the horizontal direction in order to identify an obstacle in the immediate surroundings of the aircraft, mainly in front of the cockpit and in front of the wings. This beam is concentrated in the vertical direction and angled down towards the ground in order to minimize the risks of dazzling runway personnel that encounter the beam.
The lighting systems according to the prior art, carried onboard aircraft, have a certain number of notable disadvantages.
First, the lights used are fixed. Their orientation can therefore never follow the angular variations in the incidence of the aircraft during the landing and takeoff phases, notably during variations in the direction or strength of the prevailing winds. The attitude of the aircraft may, in this respect, vary significantly when the direction or strength of the prevailing wind varies, although it is necessary to obtain good precision in the aim of the beam of light. The lighting thus achieved on the runway may vary greatly and lack effectiveness.
Second, as indicated hereinabove, the set of equipment that performs the various lighting functions described hereinabove is generally made up of distinct optical units, thereby contributing to increasing the overall mass of the lighting systems carried onboard an aircraft. Now, as is known, in the field of aeronautics, mass is a critical parameter.
Moreover, the electrical consumption, the size and the number of locations needed to perform lighting that is satisfactory with respect to the demanded performance, impose notable constraints on installation and supply of electrical power.
Finally, simultaneously switching on the landing and takeoff beams may impair the visual perception of the pilots by reducing the contrast in the zones being observed.